Freehand Ultrasound Elastography with a 3-D Probe

This paper presents the first near-real-time freehand ultrasound elastography system using a (3-D) mechanical probe. Acquisition is complete within two sec, and only an additional 20 sec are required for generation of a full 3-D strain volume. The strain is axial, with estimates of lateral and elevational tissue movement used to increase the accuracy of the axial strain measurement. This is the first time all system components have been extended to 3-D, i.e., 3-D windows are used to track displacement, which is tracked in all directions, and 3-D kernels are used for least-squares gradient estimates. Normalization of the freehand 3-D strain data is also applied across the whole volume. The system is tested using a novel research 3-D radiofrequency (RF) system with real-time control over the stepper motor driving the ultrasound probe, and real-time streaming of RF ultrasound data. The paper proves the concept, rather than making significant comments on the achievable accuracy in 3-D, although we demonstrate that the high performance of the 2-D techniques that we extend appears to carry through to in-vitro and in-vivo 3-D data. The result is a fast and high-resolution 3-D image of normalized axial strain. (E-mail: gmt11@eng.cam.ac.uk)